In various processes such as etching, deposition, oxidation and sputtering in the course of manufacturing a semiconductor device or a FPD (Flat Panel Display), plasma is widely used to allow a processing gas to make a good reaction at a relatively lower temperature. In such a plasma process, a high frequency power (RF) or a microwave is used to electrically discharge or ionize the processing gas within a decompression processing vessel.
A capacitively coupled plasma processing apparatus includes an upper electrode and a lower electrode arranged in parallel to each other within a processing vessel. A processing target substrate (e.g., a semiconductor wafer, a glass substrate, etc) is mounted on the lower electrode, and a high frequency power having a frequency (typically, about 13.56 MHz or higher) suitable for plasma generation is applied to the upper electrode or the lower electrode. Electrons are accelerated by a high frequency field generated between the two facing electrodes by applying the high frequency power, and plasma is generated as a result of ionization by collision between the electrons and a processing gas. Through a gas phase reaction or a surface reaction of radicals or ions included in the plasma, a thin film is formed on the substrate, or a material or a thin film on a surface of the substrate is etched. That is, the radicals or ions incident on the substrate play an important role in the plasma process. Especially, it is important that the ions have a physical operation caused by an impact generated when the ions are collided with the substrate.
Conventionally, in a plasma process, a RF bias method is widely employed. In this RF bias method, a high frequency power having a relatively low frequency (typically, about 13.56 MHz or lower) is applied to the lower electrode on which the substrate is mounted, and ions in the plasma are accelerated and attracted to the substrate by a negative bias voltage or a sheath voltage generated on the lower electrode. In this way, by accelerating the ions in the plasma and bringing them into collision with the surface of the substrate, a surface reaction, anisotropic etching or modification of a film may be facilitated.